Orthodontic treatment involves movement of malpositioned teeth to orthodontically correct positions. Tiny orthodontic appliances known as brackets are connected to exterior surfaces of the patient's teeth, and an archwire is placed in a slot of each bracket. The archwire forms a track to guide movement of the teeth to desired positions for correct occlusion. End sections of the archwire are often received in appliances known as buccal tubes that are fixed to the patient's molar teeth. In recent years it has become common practice to use adhesives to bond orthodontic appliances to the surface of the tooth, using either direct or indirect methods. A variety of adhesives are available to the practitioner for bonding brackets to tooth surfaces, and many offer excellent bond strengths. High bond strengths are desirable for maintaining adhesion of the bracket to the tooth surface over the duration of the treatment process, which can typically be two years or more.
However, orthodontic adhesives with high bond strengths can lead to other difficulties. For example, one of the most difficult aspects of the orthodontic treatment process can be the removal of the bracket after completion of treatment. It is well known in the industry that certain adhesives, used in combination with certain rigid brackets, are capable of causing enamel fracture under some debonding conditions. As a result, many commercially available ceramic brackets have been designed for the bond to fail at the interface between the bracket and the adhesive to prevent damage to the tooth surface during the debonding process. However, this approach results in most of the cured adhesive pad being left behind on the tooth surface after the bracket has been removed. Removal of the adhesive pad, which is typically hard and heavily crosslinked, can be time consuming for the clinician and uncomfortable for the patient.
New adhesives and methods are needed that offer satisfactory adhesion of the bracket to the tooth surface throughout the treatment process, and also allow for more convenient removal upon completion of the treatment.